Fuel-range liquid hydrocarbon products from catalytic deoxygenation of mixtures of fatty acids obtained from the hydrolysis of rapeseed oil

Abstract

The combined hydrolysis–deoxygenation method reported here demonstrates the efficiency of hydrogen-free catalytic conversion of lipid-derived multi-fatty acids into renewable drop-in hydrocarbon biofuels. Using a 5 wt% Pt on carbon (5 wt% Pt/C) catalyst for a detailed deoxygenation study, experiments were conducted in a batch reactor under nitrogen atmosphere at various temperatures (350–400 °C), reaction times (0–3 h) and catalyst/feedstock mass ratios (0–0.2). The Pt/C catalyst showed remarkable selectivity towards the decarboxylation mechanism, as evidenced by substantial CO₂ formation. The Pt/C-catalysis optimal conditions were: 400 °C, 2 h reaction time and a catalyst/feedstock mass ratio of 0.2, resulting in a yield of 3.76 wt% gasoline, 14.7 wt% kerosene and 53.7 wt% diesel range hydrocarbons. Under the set of optimal conditions, five other catalysts with different supports were tested and the results showed that 5 wt% Pt/MgSiO₃ and 5 wt% Pt/Al₂O₃ catalysts enabled complete conversion of fatty acids (total acid number = 0 mg KOH g⁻¹). In contrast, 5 wt% Pt/SiO₂, 5 wt% Pd/MgSiO₃ and bimetallic 10 wt% Ni–Cu/Al₂O₃ performed poorly, indicating the effects of both the active metal and metal–support interaction on the conversion of fatty acids. In all cases, the oil products were dominated by heptadecane, originating from decarboxylation and in situ hydrogenation of the dominant oleic acid (74.4 wt%) and other C₁₈ fatty acids present in the hydrolysed feedstock. Visually, only the Pt/C catalyst produced light-coloured liquids with direct-use fuel appeal, possibly due to its mildly acidic nature and comparably much larger surface area of 650 m² g⁻¹.